Lithium mixed metal oxides have been used as positive electrode active materials for nonaqueous electrolyte secondary batteries, particularly as positive electrode active materials for lithium secondary batteries. Lithium secondary batteries have already been used practically as small-sized power sources for cellular phone application, notebook computer application, and so on, and moreover their application has been attempted also in medium-sized or large-sized power sources for automobile application, electric power storage application, and so on.
As a conventional lithium mixed metal oxide, a lithium-nickel-manganese mixed oxide having a layered structure is disclosed in Patent Document 1. It has been reported therein that mixed oxides were obtained by mixing a transition metal mixed compound obtained by a coprecipitation method with lithium hydroxide and calcining the mixture in the air at 900° C. for 12 hours.
Patent Document 2 discloses a lithium-nickel-manganese mixed oxide and a lithium-cobalt-manganese mixed oxide. It has been reported therein that a mixed oxide was obtained by heat-treating a precursor of a mixed oxide where the precursor was obtained using a spray drying process.